Adhesive transdermal patches, which deliver drugs to a recipient by passively diffusing drugs through the recipient's skin, have been available for several decades. These patches are used to treat systemic illnesses and are the predominant transdermal drug delivery technology approved by the FDA. During the past several decades, transdermal patches have become a proven technology that offers significant benefits compared to other delivery techniques. For example, transdermal patches may provide a finer level of control when releasing drugs into a patient. This feature may provide a steady blood-level profile which may in turn reduce systemic side effects and improve efficacy compared to other delivery techniques. Transdermal patches may also be more user-friendly, convenient, and painless than other delivery techniques. For this reason, transdermal patches are typically associated with improved patient compliance.
There is currently a significant amount of research being dedicated to improving techniques for transdermally delivering drugs using transdermal patches. For example, research has shown that complex chemical enhancers may be incorporated into delivery systems to improve transdermal drug delivery. Other research has shown that physical phenomena such as electricity (iontophoresis), ultrasound (phono- or sonophoresis), or magnetism may be used in a transdermal device to improve drug delivery. A highly effective although simpler mechanism for improving transdermal drug absorption, however, is the application of heat.
Heat application may improve transdermal drug delivery by increasing the permeability of skin, blood vessel walls, and rate-limiting membranes. Heat may also improve transdermal drug delivery by increasing the circulation of body fluids. Heating the skin dilates pathways in the skin, increases thermodynamic drive, increases the kinetic energy and movement of particles in the treated area, and facilitates drug absorption into the vascular network. This may improve systemic delivery while decreasing localized delivery as drug molecules are transported away from the delivery site.
Currently, various patches are being marketed or developed to apply heat to the skin and thereby increase drug absorption. Some of these patches generate heat using exothermic chemical reactions while others use electric heating elements coupled to control devices. Many of these patches are more complex than they need to be and may require several components (e.g., separated drug and heater portions). Patches that use exothermic reactions to produce heat may use chemical reactants or produce reaction products that are incompatible with the skin, thereby requiring isolation from the skin. Other patches may fail to take advantage of exothermic chemical reactants or reaction products that may be beneficial to the skin or body.
In view of the foregoing, what are needed are apparatus and methods to enhance the transdermal delivery of medicines and other beneficial agents. More specifically, apparatus and methods are needed to reduce the complexity, and thus the cost, of current transdermal patches. Further needed are transdermal patches that use exothermic chemical reactants or produce reaction products that are compatible with the skin, and thus do not require isolation from the skin. Further needed are transdermal patches that can take advantage of exothermic chemical reactants or reaction products that may be beneficial to the skin or body.